1. Field of the Invention
This invention relates to multicomponent structures; and more particularly to multicomponent structures having improved adhesion.
2. Description of the Prior Art
It is known in the art to produce multicomponent structures to take advantage of different properties exhibited by the various components in the structure. Typical of multicomponent structures are multilayer films in which different layers have specific characteristics.
For example, in packaging applications, it is desirable to use fluoropolymers which are known for their inertness to most chemicals and resistance to high temperatures as well as low coefficients of friction. Polychlorotrifluoroethylene (xe2x80x9cPCTFExe2x80x9d) homopolymers and copolymers, and ethylene-chlorotrifluoroethylene (xe2x80x9cECTFExe2x80x9d) alternating copolymers, are particularly advantageous due to their excellent barrier properties. However, use of such fluoropolymers is restricted to specialty packaging applications due to their relatively high cost.
A suitable means of reducing the cost of a packaging material fabricated from a costly polymer is to form multilayer structures in which the polymer layer is either coextruded or laminated with other, less costly, polymer layers. This approach is particularly desirable for fluoropolymer packaging applications since a thin layer of the fluoropolymer is often all that is needed to take advantage of the desirable properties of the fluoropolymers while minimizing the cost. However, fluoropolymers do not adhere strongly to most other polymers; in fact, most fluoropolymers are known for their non-stick characteristics.
Use of functionalized polyolefins as the adhesive layer in multicomponent structures has been described; see for example U.S. Pat. Nos. 4,677,017 and 5,139,878, the disclosure of which is expressly incorporated herein by reference. While these multilayer structures exhibit excellent moisture and barrier properties, in many instances, they lack sufficient adhesive strength to have any significant use. As a result, there are not yet any commercially available coextruded halopolymer films. It would therefore be desirable to provide an improved adhesive resin in order to provide superior multicomponent structures suitable for a wide variety of applications.
In accordance with this invention, there is provided a multicomponent structure comprising at least one halopolymer layer and at least one adhesive layer wherein the adhesive layer is a soft, modified polymer comprising a base polymer having at least one functional moiety selected from the group consisting of unsaturated acids and anhydrides thereof, amines and epoxy compounds, wherein said adhesive layer has an ASTM D-2240 shore hardness number of less than about 25 in the D scale and less than about 75 in the A scale. Preferably, the shore hardness number is less than about 20 in the D scale and less than about 72 in the A scale. It is also preferable that the adhesive be highly modified with the functional moiety. Adhesives which are modified with maleic anhydride are particularly advantageous in the practice of this invention. In a preferred embodiment, the multilayer structure is a three layer structure which, most preferably, is a three layer film.
It has unexpectedly been found that when soft polymers with a high degree of modification are used as the adhesive layer in halopolymer-containing multicomponent structures, a high degree of adhesion between the halopolymer and the soft, modified polymer exists.
The adhesive layer of the present invention is formed from a base polymer having a functional moiety, and has an ASTM D-2240 shore hardness number of less than about 25 in the D scale and less than about 75 in the A scale, which polymer has been modified with an unsaturated acid, anhydride, amine or epoxy moiety in an amount of from about 0.1% to about 20% by weight based on the total weight of the polymer. In a preferred embodiment, the shore hardness number is less than about 20 in the D scale and less than about 72 in the A scale. Shore hardness number is measured by the American Standard Test Method (ASTM) D-2240 which is well known to those skilled in the art. As used herein, shore hardness number is determined by the shore hardness test and is based on the penetration of a specific type of indentor when forced into specific materials under specific conditions. Shore hardness number is an inverse function of indentor extension which is dependent on the elastic modulus and viscoelastic behavior of the material. Thus, the softer a material, the lower shore hardness number. There are different types of durometers used in shore hardness tests, among which Type A and Type D are commonly reported. The difference of these two types are based on the shape of the indentor and the applied force. For example, an indentor of a Type D Durometer has a sharper point (i.e., 0.100xc2x10.012 mm R) than a Type A Durometer (i.e., 0.79xc2x10.03 mm R).
The functional moiety of the adhesive layer comprises from about 0.2% to about 15%, preferably from about 0.5% to about 10%, and most preferably from about 1% to about 5% by weight based on the total weight of the polymer. Any unsaturated acid or anhydride may be used as the functional moiety in this invention. Suitable acids include unsaturated carboxylic acids such as maleic acid, fumaric acid, crotonic acid, citraconic acid and itaconic acid. Suitable anhydrides include anhydrides of any of the foregoing. Of these, the most preferred is maleic anhydride. Suitable amines include aliphatic or aromatic, primary, secondary and tertiary amines. Specific examples include: 2,4,6-tribromoaniline, methylamine, ethylamine, propylamine, dimethylamine-N-methylanaline, ethylmethylamine, 2-(N-methylamine)heptane, sec-butyldimethylamine, N-ethyl-N-methylaniline, trimethylamine, and N,N-dimethylanaline. Suitable epoxy compounds are those having from about 2 to about 20 carbon atoms. In a particularly preferred embodiment, the adhesive layer comprises about 1% to about 5% of maleic anhydride.
Base polymers which are useful in the preparation of the adhesive layer include, but are not limited to, poly(xcex1-olefin) homopolymers, copolymers, and mixtures thereof, and thermoplastic elastomers including styrenic block copolymers, olefinic elastomers, elastomeric alloys, thermoplastic polyurethanes, elastomeric polyesters and elastomeric polyamides.
Poly(xcex1-olefin) homopolymers can be prepared from xcex1-olefins having from about 2 to about 10 and preferably from about 2 to about 6 carbon atoms, and include polyethylene (including ultra low density, low density, linear low density, medium density, high and ultra high density), polypropylene, polybutylene, polybutene-1, polypentene-1, poly-3-methylbutane-1, poly-4-methylpentene-1, and polyhexene. Copolymers of two or more of the foregoing xcex1-olefins or xcex1-olefins and other monomers such as alkyl esters of xcex1,xcex2-ethylenically unsaturated carboxylic acids are useful in the practice of this invention, see for example, U.S. Pat. No. 5,139,878, the disclosure of which is expressly incorporated herein by reference.
Styrene block copolymers may be linear or branched and include styrene and butadiene (SBS), styrene and isoprene, styrene and ethylene-butylene (SEBS), and styrene and ethylene-propylene.
Suitable olefinic thermoplastic elastomers include ethylene propylene diene (EPDM) and ethylene propylene rubber.
Suitable elastomeric alloys include melt processable rubbers, thermoplastic vulcanizates, such as ethylene propylene rubber or nitrile rubber and polyolefin in which vulcanized rubber is intimately dispersed in the polyolefin matrix, and ethylene interpolymers, such as polyethylene alloyed with polypropylene or polyethylene where the polyethylene is crosslinked.
Suitable elastomeric polyesters include copolymers of polyester and polyether. Suitable polyesters include poly(ethylene terephthalate) (PET), poly(butylene terephthalate) (PBT) and PET/PBT copolyesters. Suitable polyethers are those having from about 2 to about 20 carbon atoms.
Suitable thermoplastic polyurethanes include polyester-based or polyether-based polyurethanes. Specific examples include Estane 58113 (polyester-based), Estane 58013 (polyether-based) and Estane 58880 (polyether-based) all available from B. F. Goodrich and Pellethane 2103-70A (polyether-based) elastomer available from the Dow Chemical Company.
Suitable elastomeric polyamides include copolymers of a polyamide and a polyether. Suitable polyamides include nylon 6, nylon 1, nylon 12, nylon 6,6, nylon 4,6, nylon 6,9, nylon 6,10, nylon 6,12, and nylon 6,6T. Suitable ethers are those having from about 2 to about 20 carbon atoms.
Preferred base polymers include olefinic thermoplastic elastomers, and poly(xcex1-olefin) homopolymers, copolymers and mixtures thereof.
These base polymers can be substituted in any position with any of the following compounds: halogen (including chlorine, fluorine and bromine), oxygen and nitrogen.
A particularly effective composition is a ethylene-propylene elastomer (EP rubber) modified with about 2% to about 4% of maleic anhydride, comprising approximately 80% ethylene component and 20% propylene component in the overall composition. The ethylene-propylene elastomer can be either a copolymer or a blend with different levels of E/P composition and/or E/P sequence, in which at least one of the components in the blend is modified with unsaturated carboxylic acids and anhydrides. An example is a two-component blend, in which one component is an essentially EP random copolymer or ethylene-xcex1-olefin copolymer without any modification, and the other is an EP block copolymer or crystalline polyethylene modified with a high level of maleic anhydride. The latter component can be also a terpolymer, consisting of ethylene, propylene, and maleic anhydride.
The soft, modified polymers of the invention can be prepared by conventional methods well known in the art, including, but not limited to, copolymerization and grafting processes. See, for example, U.S. Pat. Nos. 3,481,910; 3,480,580; 4,612,155; and 4,751,270, the disclosures of which are expressly incorporated herein by reference.
The halopolymers with which the soft, modified polymers can be used are known in the art and all are commercially available. They include, but are not limited to, fluoropolymers, chloropolymers and fluorochloropolymers having from about 2 to about 20 carbon atoms wherein at least one carbon atom in the polymer is substituted with at least one halogen atom.
Specific examples of suitable halopolymers include: PCTFE homopolymers and copolymers, ECTFE copolymer, ethylene tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymers (FEP), perfluoroalkoxy polymer (PFA), poly(vinylidene fluoride), poly(vinyl fluoride), poly(vinylidene chloride), poly(vinyl chloride), copolymers or blends of tetrafluoroethylene, and copolymers or blends of vinylidene fluoride and blends of 2 or more of the foregoing.
Preferred halopolymers include PCTFE homopolymers and copolymers, ECTFE copolymer, ethylene tetrafluoroethylene copolymer, fluorinated ethylene-propylene copolymers (FEP), copolymers or blends of tetrafluoroethylene, and copolymers or blends of vinylidene fluoride.
The soft modified polymers may be used with halopolymers to prepare multicomponent structures including coextruded articles such as film and tubing, laminates such as film and sheet, and injection and blow molded articles.
The soft modified polymers produced in accordance with the teachings herein are suitable for the manufacture of multicomponent structures and, in particular, multilayer films. The multilayer films may be prepared by methods well known in the art. (See e.g., U.S. Pat. No. 4,677,017, the disclosure of which is expressly incorporated herein by reference and the foregoing Examples) and may be oriented in one or both directions, or unoriented. (See U.S. Pat. No. 4,362,585, the disclosure of which is expressly incorporated herein by reference). The multilayer films include at least one halopolymer layer and at least one adhesive layer adjacent to the halopolymer layer. Suitable film structures include, but are not limited to: A/B/C, A/B/C/B/A and C/B/A/B/C wherein A is a halopolymer, B is an adhesive layer and C is a thermoplastic polymer. In a more preferred embodiment, the film structure has at least three layers; one halopolymer layer, one adhesive layer adjacent to the halopolymer and one thermoplastic polymer layer adjacent to the soft, modified polymer. PCTFE is a preferred halopolymer for these three layer films. Such a film is particularly useful in the packaging of pharmaceutical and other materials, such as those materials requiring blister packaging.
Thermoplastic polymers which may be added to the halopolymer/tie layer structure include polyamides such as crystalline and amorphous nylon, e.g. nylon 6 and MXD6 (available from Mitsubishi Gas Chemical Company, Inc.); polyesters such as poly(ethylene terephthalate), 1,4-cyclohexanedimethanol modified poly(ethylene terephthalate), poly(1,4-cyclohexanedimethylene terephthalate), poly(butylene terephthalate), poly(ethylene naphthalate) and poly(butylene naphthalate); polyolefins such as polyethylene, polypropylene and polybutene, and the other polyolefins mentioned above with respect to the base polymers; polyacrylonitrile, polystyrene, polyacrylates, poly(vinyl chloride), poly(vinylidene chloride), ethylene vinyl acetate, polyurethanes, and copolymers or blends thereof.
Naturally, other additives which are normally included in multicomponent structures can be included in the structures of this invention. They include UV absorbers and stabilizers, fillers, slip additives, antioxidants and heat stabilizers.
As noted above, the material of the invention can be used to prepare multicomponent structures other than film. These structures can be prepared by coextrusion, lamination, injection molding and blow molding. All of these processes are known in the art; see e.g. U.S. Pat. Nos. 5,139,878; 4,677,017; and 4,510,301, the disclosures of which are expressly incorporated herein by reference. For example, the multicomponent structures of the present invention can be used to prepare multicomponent tubing, either symmetrical of asymmetrical, which comprises at least one halopolymer layer and at least one adhesive layer adjacent to the halopolymer layer. In a preferred embodiment, the tubing comprises at least one halopolymer layer, at least one adhesive layer adjacent to the halopolymer layer and at least one thermoplastic polymer layer adjacent to the adhesive layer. Suitable structures for the tubing include, but are not limited to: A/B/C, A/B/C/B/A and C/B/A/B/C wherein A is a halopolymer, B is an adhesive layer and C is a thermoplastic polymer layer.
In another embodiment, the invention relates to a method of improving the adhesion of halopolymers to other polymers in multicomponent structures comprising utilizing a soft, modified polymer as an adhesive layer between the halopolymer and the other polymer.
It was surprisingly found that multicomponent structures produced in accordance with the teachings herein exhibited superior interlayer adhesion than multicomponent structures utilizing the adhesive resins of the prior art.